Temperature compensating hydraulic tappet



Dec. 13, 1966 R- D. CORNELL TEMPERATURE COMPENSATING HYDRAULIC TAPPET Filed June 16, 1965 INVENTOR. (Wm/4w a (UK/V514 BY m a a z W WM w a Z ATTORNEYS United States Patent ()filice 3,291,107 TEMPERATURE COMPENSATING HYDRAULIC TAPPET Richard D. Cornell, Muskegon, Mich, assignor to Johnson Products, Inc., Muskegon, Mich, a corporation of Michigan Filed June 16, 1965, Ser. No. 464,449

2 Claims. (Cl. 12390) This invention relates to valve lifter tap-pets for internal combustion engines, and more particularly to a temperature compensating hydraulic tappet assembly. I The great bulk of tappets for many years have been made of basic cast iron materials. In a hydraulic tappet assembly therefore, a cast iron hollow tappet body encloses a steel hollow plunger element which has a valve seat on one end. A small clearance exists between these two elements, allowing discharge of oil from the tappet. As is known, when the engine is cold, the oil in the tappet usually has a greater viscosity than when the engine becomes warm. Hence, the amount of oil flow that occurs through this clearance when the engine is warm is much greater than that which occurs when it is cold.

A tappet which would automatically compensate for temperature changes so as to obtain more constant oil flow was suggested over three decades ago. In fact, it is disclosed in Burkheart Patent No. 1,916,191. The suggestion is to use an aluminum plunger in a cast iron body so that the different thermal expansion of the components would accommodate changes in oil viscosity by changing the clearance between these two elements. This concept has some attraction, but is not commercially practical or acceptable. The aluminum plunger wears very rapidly and is very highly corrodible, so that, if used, the life of the tappet is so extremely short that it is not practical.

Tappets are very high speed units. They must have good wear qualities and good corrosion resistance.

An aluminum tappet plunger suggested heretofore is not only subjectto rapid wear, but is highly susceptible to structural failure because of its low structural strength. Its surfaces are also highly malleable so as to readily deform when force is repeatedly applied. The forces imparted to the tappet element are very substantial.

Consequently, the automotive industry is still in need of a practical, long life, temperature compensating hydraulic tappet, particularly one with a relatively low inertial drag. However, to be practical, this temperature compensating tappet must have good structural strength, must have excellent resistance to wear, have good resistance to corrosion, have low malleability on contact surfaces, and must necessarily be capable of mass production fabrication without special inserts and the like to strengthen it or form contact surfaces.

It is an object of this invention to provide such a tappet, i.e. a tappet that is temperature compensating to allow relatively constant oil flow whether the engine is cold or hot, that has a very long useful life, that has excellent corrosion resistance, and that is capable of mass production fabrication by practical fabricating and treating techniques.

Another object of this invention is to provide a tappet that, for the first time as far as is known, actually achieves a practical temperature compensating hydraulic tappet while also having a long useful life and excellent wear and support characteristics. The concept and structure of the novel tappet are relatively simple, once understood. Indeed, this very simplicity is one of its major attributes, especially in view of its tremendous commercial significance, and the practical results obtained.

These and other objects of this invention will become form thickness over its extent.

3,29Ll07 Patented Dec. 13, 1966 apparent upon studying the following specification in conjunction with the drawings, in which:

FIG. 1 is a sectional, elevational view of the novel tappet;

FIG. 2 is an enlarged, fragmentary, sectional view of a portion of the device in FIG. 1 showing the clearance when the engine is cold; and

FIG. 3 is an enlarged, fragmentary, sectional view of the portion in FIG. 2 showing the clearance when the engine is warm.

Referring now specifically to the drawings, the complete tappet assembly 10 includes an elongated tappet body 12 having a closed end 14 with a cam follower surface 16, and an opposite open end 13. Inside the axially elongated chamber formed in this hollow body is sli-dably fitted a hollow plunger 20. This plunger has an annular nose portion 22 on its lower inside end adjacent closed end 14 of the tappet body. Through this nose is a passageway 24 which communicates between hollow chamber 26 inside the plunger, and the pressure chamber 28 in the tappet body. A fiat valve plate or disc 30 abuts against this nose, and is held in biased relationship against it by a small compression coil spring 32. This coil spring is held against this valve plate by a cup shaped retainer stamping 34. This stamping is held against the end of the plunger, around nose 22, by a larger coil compression spring 36 which has one end abutting the closed body end 14.

Into the open end of the plunger is a push rod seat element 38. This element has a push rod seat concavity 40 in its outwardly facing end, to receive the end of push rod 42. Element 38 retains a flat orificed disc 44 against an inner shoulder in plunger 20 to serve as a metering valve of the type described and claimed in US. Patent No. 3,128,749. The entire assembly may be retained in this housing by an annular snap ring 46.

Fluid flow occurs through hollow push rod 42 and through passageway 48 in push rod seat element 38, past metering disc 4d. It also occurs through passage port 50 in the side of body 12, around annular passageway 52, and through port 54- into the chamber of the plunger.

In accordance with this invention, the tappet body is formed of cast iron. Hence, it has a relatively low thermal expansion with change in temperature.

The plunger 20, on the other hand, is formed of aluminum with a special overall enveloping jacket. The plunger is specially treated to have particular corrosion and wear characteristics. Specifically, it is treated to have a complete eveloping casing over its entire surface area so that it is jacketed in its entirety. This case extends integrally over outer peripheral surface 20a, inner peripheral surface 2%, and end surface 20c on nose 22 and is of uni- This hardened case cornprises a uniform layer of at least 0.0005 inch, and up to about 0.0025 inch of hard anodized aluminum oxide. This causes a tremendous wear resistance, corrosion resistance, and high support of outer portions of the entire plunger. This makes the basic aluminum core structure usable for this high speed member. The resulting support to the encased plunger is exceptional, and enables normal, repeated forces and blows to be taken without structural failure. Its wear resistance is greater than that of heat treated steel, cyanide hardened steel, and hard chrome plate. It has excellent hardness, for example, of seven to nine as measured on the Mohs scale. It has a very small coefficient of friction, particularly when finish ground, honed, or lapped. Its corrosion resistance is excellent, for example about two to four thousand times that of normal decorative anodized aluminum with its usual extremely thin layer. Salt spray tests show comparable anodized aluminum to have corrosion resistance for only 250 to 500 hours, whereas the hard cased aluminum oxide plunger to have resistance for 12,000 hours or more under comparable conditions.

The enveloping case thickness is constant over plane and curved surfaces, and in recesses, bores and undercuts. Exacting tolerances can be achieved by normal finishing techniques. The case also constitutes a thermal insulator, increasing the erosion resistance of the material to intermittent flame impingement. It will not spall or peel off like a plated surface and exhibits excellent anti-seizing properties.

Due to the difference in thermal expansion rate of the uniform jacket and the inner core of aluminum metal, minute crazing of the case occurs over the plunger body with temperature changes. Extensive experimental use has shown, however, that this has no detrimental effects on the operational characteristics of the structure. The strength, resistance, and other noted properties still avail.

In the novel construction, it has been found that with the entire exposed surface of the plunger uniformly treated to have this aluminum oxide encasement, its surfaces contacting the push rod seat are not significantly malleably deformed during its long useful life, even though these surfaces are frequently exposed to considerable hammering action.

The outer peripheral surface 20a of the plunger, immediately adjacent the inner peripheral wall of the tappet body is honed, lapped, or ground to an exact dimension for tolerances, and to effect a smooth, wear resistant, less friction bearing surface.

The case enables the desired expansion and contraction of the aluminum plunger to achieve the desired variable temperature compensating effects. Referring more specifically to FIGS. 2 and 3, for example, the clearance C1 between the plunger and the tappet body existing when the structure and oil are cold" is substantially larger than the clearance C2 existing between these two elements when the engine and oil are Warm. This clearance varies inversely in size in general proportion to engine temperature, to control oil flow to a relatively constant value.

With expansion of the plunger core, the crust 202 on the plunger also expands. During this expansion, even though the noted minute crazing occurs over its surface because of its smaller expansion coeflicient that that of the aluminum core, it still maintains a completely integral relationship with the aluminum metal to serve in overall strengthening, bearing surface characteristics, etc.

Hence, in operation of the novel tappet, with hydraulic fluid flowing through the tappet in conventional manner, flow of oil between the plunger and the valve body from the pressure chamber 28 is maintained under a relatively constant controlled flow relationship whether the engine is hot or cold. This structure achieves for the first time, as far as is known, a practical temperature compensating, hydraulic tappet having a long useful life with tremendous resistance against wear and corrosion. It also has a relatively lightweight construction achieving lower inertia than conventionally encountered.

Further to be noted is the fact that no special inserts or the like are necessary even though the plunger is made of aluminum. The fiat plate valve 30 is in direct abutment with the nose of the plunger, and specifically with the case which encompasses this nose as well as every other exposed surface of the plunger.

Certain additional advantages to this invention may occur to those in the art upon studying this foregoing description, Also, certain minor details of construction could conceivably be made in the preferred form of the device without departing from the novel concept presented. It is realized that the concept and the structure, when once understood, are quite simple in nature, and indeed this is one of the chief attributes of the construction, particularly in view of the unique practical results obtained and the tremendous commercial advantages achieved. Therefore, this invention is intended to be limited only by the scope of the appended claims and the reasonably equivalent structures to those defined therein.

I claim:

1. In a temperature compensating hydraulic tappet for an internal combustion engine, having a hollow tappet body having one closed end with an outer cam follower surface, and one open end, and axially movable plunger in said body, said plunger having an outer peripheral surface spaced slightly from said body to form an oil passage therebetween, said plunger being hollow, with an inner peripheral surface, and having a passageway opening and an integrally formed valve seat on its inner end and a push rod seat receiving opening on its opposite end adjacent said body open end; said tappet body comprising a cast iron body having a relatively low thermal expansion rate; said plunger having an aluminum core with a relatively high thermal expansion rate, and having an integral, hard surface, enveloping case jacket of 0.0005 to 0.0025 inch thickness of aluminum oxide over its entire surface area including said valve seat, said jacket effecting strength reinforcing for the entire plunger.

2. A temperature compensating hydraulic tappet for an internal combustion engine, comprising: a hollow tappet body having one closed end with an outer cam following surface and one open end; an axially movable plunger in said body; said plunger having an outer peripheral surface spaced from said body; said plunger being hollow, with an inner peripheral surface, and having a passageway opening and an integrally formed valve seat on one end of said plunger and a push rod seat receiving opening on its opposite end adjacent said body open end; a spring biased valve on said valve seat; said tappet body being a cast iron body having a relatively low thermal expansion rate; said plunger having an aluminum core with a relatively high thermal expansion rate, and having an integral, hard surface, case jacket of aluminum oxide over its entire inner and outer surface area; said plunger having a nose portion around said passageway opening forming an annular planar configuration for said valve seat; said case forming an integral aluminum oxide hardened surface on said valve seat in direct abutment with said valve; said valve being a fiat plate biased into direct abutment with said seat; said case effecting a strength reinforcing jacket for the entire plunger, expandable and contractible integrally with expansion and contraction of said plunger, and said case on said outer peripheral surface being surface finished to form a hard, smooth bearing surface.

References Cited by the Applicant UNITED STATES PATENTS 1,916,191 7/1933 Burkhardt 12390 2,932,290 4/ 1960 Christensen 12390 3,079,903 3/1963 Humphreys l23--90 3,090,367 5/1963 Ayres 12390 3,200,801 8/1965 Dornbos 123-90 MARK NEWMAN, Primary Examiner.

AL LAWRENCE SMITH, Examiner, 

1. IN A TEMPERATURE COMPENSATING HYDRAULIC TAPPET FOR AN INTERNAL COMBUSTION ENGINE, HAVING A HOLLOW TAPPET BODY HAVING ONE CLOSED END WILL AN OUTER CAM FOLLOWER SURFACE, AND ONE OPEN END, AND AXIALLY MOVABLE PLUNGER IN SAID BODY; SAID PLUNGER HAVING AN OUTER PERIPHERAL SURFACE SPACED SLIGHTLY FROM SAID BODY TO FORM AN OIL PASSAGE THEREBETWEN, SAID PLUNGER BEING HOLLOW, WITH AN INNER PERIPHERAL SURFACE, AND HAVING A PASSAGEWAY OPENING AND AN INTEGRALLY FORMED VALVE SEAT ON ITS INNER END AND A PUSH ROD SET RECEIVING OPENING ON ITS OPPOSITE END ADJACENT SAID BODY OPEN END; SAID TAPPET BODY COMPRISING A CAST IRON BODY HAVING A RELATIVELY LOW THERMAL EXPANSION RATE; SAID PLUNGER HAVING AN ALUMINUM CORE WITH A RELATIVELY HIGH THERMAL EXPANSION RATE, AND HAVING AN INTEGRAL, HARD SURFACE, ENVELOPING CASE JACKET OF 0.0005 TO 0.0025 INCH THICKNESS OF ALUMINUM OXIDE OVER ITS ENTIRE SURFACE AREA INCLUDING SAID VALVE SEAT, SAID JACKET EFFECTING STRENGTH REINFORCING FOR THE ENTIRE PLUNGER. 